Rigid to FS possible?

I am just getting into xc riding. Right now I'm using my dad's old ('94) cannondale m700. It's a rigid frame and I quite like it minus the lack of front suspension. I guess the main things I like about it are my riding position (more stretched out rather than upright), and more importantly it's light weight (about 25lbs). It's pretty stock except for some semi-slick tires (I use it as a commuter too), some cheap shimano brake lever/shifter (all-in-1 assembly), and avid SD-7 v brakes). I'd like to buy a new bike, but don't really have the money, plus I'm not sure if I should spend the money until I get a little more into the sport.

What I'd like to do is add front suspension, while keeping the bike as light as possible (was thinking maybe a rockshox SID). But I'm not really sure if this would be possible?? I keep hearing it might change the geometry (but I don't really understand what that will do/cause to the bike). The factory fork is a cannondale pepperoni.

that bike was rigid

You could measure the A-C (axle to crown) length, and then try to match that up with a SID or similar, you may be looking for some pretty low suspension numbers like 60mm though, I'm just not sure. An 80mm would likely be OK, but check it out 1st before buying anything. A good Cdale LBS might be your best resource, especially if there's a really good mechanic that remembers that far back, or knows Cdale well.

The frame may/may not have been designed to handle a fork, but I don't know how to check that far back.

It is more than likely not suspension corrected geometry (OP: meaning an axle to crown length than mimics a suspension fork). I have a '94 Trek 7000 which was a decent level of Trek's back then and it has a 1-1/8" steerer and it is not suspension corrected. I don't think most manufacturers started doing suspension corrected rigid forks until '96 or so.

Like someone else mentioned, measure your axle to crown of your current fork and compare that to a shorter 80mm travel fork to see how far off you are. If it was designed for a suspension fork it was more than likely a 63mm travel fork, might find one on ebay.

The geometry that will be thrown off if the bike is not made for it will be a slacker head tube angle and seat tube angle. It will affect the steering and climbing capabilities of the bike. How much will depend on how much longer the suspension fork is over the rigid fork. Some people are going to tell you that you wont notice the change, but other people the change will drive them crazy. It could also put a lot of stress on the head tube that it was not designed for. Again depending on the amount of change.

Another avenue to consider is a wider pair of tires to soften the ride. They won't add anymore weight than a suspension fork, but would give you a little more cushion while keeping the ergonomics you like at a low price point.

I am just getting into xc riding. Right now I'm using my dad's old ('94) cannondale m700. It's a rigid frame and I quite like it minus the lack of front suspension. I guess the main things I like about it are my riding position (more stretched out rather than upright), and more importantly it's light weight (about 25lbs). It's pretty stock except for some semi-slick tires (I use it as a commuter too), some cheap shimano brake lever/shifter (all-in-1 assembly), and avid SD-7 v brakes). I'd like to buy a new bike, but don't really have the money, plus I'm not sure if I should spend the money until I get a little more into the sport.

What I'd like to do is add front suspension, while keeping the bike as light as possible (was thinking maybe a rockshox SID). But I'm not really sure if this would be possible?? I keep hearing it might change the geometry (but I don't really understand what that will do/cause to the bike). The factory fork is a cannondale pepperoni.

Just so you know, "FS" is generally understood to mean "full suspension". Front suspension is generally referred to as a hardtail or HT. Just want to save you some possible confusion down the road.

You could measure the A-C (axle to crown) length, and then try to match that up with a SID or similar, you may be looking for some pretty low suspension numbers like 60mm though, I'm just not sure. An 80mm would likely be OK, but check it out 1st before buying anything. A good Cdale LBS might be your best resource, especially if there's a really good mechanic that remembers that far back, or knows Cdale well.

The frame may/may not have been designed to handle a fork, but I don't know how to check that far back.

Good luck, Jim

I measured my A-C length and came up with 412mm. According to sram's website, the 2010 SID's A-C length is 453mm (at 80mm travel). Is this too far off? Also what is the offset and is it important to match that up as well?

Originally Posted by older guy

Do you have a 1" or 1-1/8" steerer tube on the Pepperoni fork? If you have a threaded fork, most probably it is 1 inch. 1 inch suspension forks are hard to come by nowadays.

To change a threaded fork to a suspension fork, you will also have to change headset, buy spacers, cap and a non-quill stem.

It's threadless (as least that's what a guy at the lbs told me). Other than JimC's link, how can I measure the size of my steerer tube? And if it does turn out to be 1.25" will I pretty much be screwed when it comes to finding a new fork?

Originally Posted by kapusta

Just so you know, "FS" is generally understood to mean "full suspension". Front suspension is generally referred to as a hardtail or HT. Just want to save you some possible confusion down the road.

OOOoooo....that''s actualy very helpful. I thought it stood for "front suspension"

Originally Posted by Reid Hollister

dude for what you'd spend for a new fork, you might as well get a new bike. It would only be a little bit more and you could get something that's much better. Hopefully with disc brakes too.

Well I saw SID's going for around $500-600 on ebay. If a new bike was only a little more then I would be up for that, provided that it was similar in weight (from the little research I've done so far, I don't think bikes in that price range are that light). I ridden heavy bikes before, and the weight really makes climbing a lot harder.

I measured my A-C length and came up with 412mm. According to sram's website, the 2010 SID's A-C length is 453mm (at 80mm travel). Is this too far off? Also what is the offset and is it important to match that up as well?

41mm is a pretty big change. That will slacken all the angles on the bike a little over 2.5 degrees. Even if you factor in the sag of the fark it is still around 2 degrees. That is going to really change the ways the bike handles. If there an option to run it at something like 60mm?

It's threadless (as least that's what a guy at the lbs told me). Other than JimC's link, how can I measure the size of my steerer tube? And if it does turn out to be 1.25" will I pretty much be screwed when it comes to finding a new fork?

There should be a top cap on the top of your stem with a single bolt in the center. If you remove it (which you can do as long as you do not loosen the stem) you can see the steer tube. Just measure to outside diameter. I think if it is 1-1/4" you can probably get some sort of reducer to bring it down to 1-1/8", but check that out first.

Well I saw SID's going for around $500-600 on ebay. If a new bike was only a little more then I would be up for that, provided that it was similar in weight (from the little research I've done so far, I don't think bikes in that price range are that light). I ridden heavy bikes before, and the weight really makes climbing a lot harder.

I would be very hesitant to drop $500-600 on a fork for this bike, especially if it is whacking out the geometry. I think you are better off saving towards a new bike. If this thing is 15 years old and mostly stock, you can expect to be replacing other things sooner than later.

I would want to be pretty sure that this bike is a keeper before dropping that kind of money on it, and if you are just getting into xc riding, then your tastes may change. Other things to consider are that you are not going to be able to put disc brakes on the rear of that bike. If you ever want to go to 8 or 9 speed you are going to have to replace the shifters (and in your case brake levers), possibly the rear wheel (that rear hub may not take an 8-9 speed cassette, someone else here may know for sure).

Also, when comparing the weight of this to a new bike, keep in mind that this has an aluminum rigid fork. Even with a Sid, I'll bet you are adding about a pound and a half to the bike. Without spending $500+ you are likely adding 2 pounds.